This invention relates to a filler unit for topping up a container with a liquid to a predetermined, desired level. In one application, the unit is suitable for use in topping up the secondary cells of batteries.
Secondary cells are traditionally topped up from time to time with suitably purified water to compensate for loss due to electrolysis and evaporation. This topping up is simple when the number of cells is small and the batteries are readily accessible, eg. car batteries etc.
With larger batteries, for example, batteries for producing tractive forces, standby power supplies, for computer and lighting duties, and so on the number of cells is often so large and the accessibility often so poor, that topping up can become particularly difficult and time consuming.
Maintenance free batteries have been developed but these are costly and not suitable for deep discharge cycling duties. Automatic topping up systems have been developed to alleviate topping up problems but they have proved insufficiently robust. Some systems have used a vacuum principle to draw water into the cells necessitating air tight cell constructions and the use of expensive pumping arrangements. Other systems have incorporated floats in direct contact with the electrolyte to detect and control the level of electrolyte. Such floats are exposed to mechanical wear and aggressive chemical attack and consequently have often proved unreliable.